This invention relates generally to devices which support and hold equipment and more particularly to a foot for such devices suitable for holding geomatic equipment and accessories.
Although the art of surveying is old, recent improvements in equipment, such as automatic electronic total surveying stations, have increased the accuracy of the surveying instruments far beyond what was possible previously. Where accepted accuracy for equipment in the not too distant past was 20 seconds of a degree, accuracy is now commonly required to be 1 second of a degree. At these levels of precision, the instruments and many of their accessories must be supported in a manner which is consistent and stable. Accordingly, there is a need for closer examination of support structure used for surveying equipment so that improvements in instrumentation will not be lessened by inadequate supports. Further, the cost of surveying equipment makes it highly undesirable to damage it by failure of the supports because of instability.
Pole supports used in the surveying field typically take the form of bipods or tripods, but conceivably any number of legs could be provided. Conventionally, it has been necessary to provide completely separate inventories of bipods and tripods to meet the needs of different customers and for different applications. Legs of these supports are usually freely pivotable about a head of the support to swing toward each other for ease of carrying the support when not in use. A support having three or more legs can support equipment or other items above and out of contact with the ground. Typically, bipods are used to support surveying equipment such as a surveying pole, which also contacts the ground, but tripods may also be used to support surveying poles. The stability of such supports can be compromised in situations where there are forces (e.g., wind and loads from the surveying equipment) acting on the support and tending to tip the support over. In that case, one of the legs is subjected to an upward force component tending to raise the leg up as the support pivots about a point(s) of contact of the other leg(s) with the ground.
Presently, there is little or no resistance provided by the legs to such upward forces other than the weight of the leg. Even if there are stakes associated with the legs that penetrate the ground, the upward force tends to be directed right along the long axis of the stakes so that they are lifted out of the ground. The problem is compounded by the fact that the legs conventionally are mounted for pivoting freely about a horizontal axis. Even if the support does not tip over, if one leg loses contact with the ground or the frictional resistance to pivoting movement of the leg becomes sufficiently small, the leg will swing in toward the center of the support. The support is unlikely to regain stability when this happens. Should the support move back toward its original position, the leg having pivoted inwardly is no longer in position to engage the ground in a stable position. The center of gravity of the combined support and surveying equipment may lie outward of the point where the leg re-contacts the ground so that the entire unit topples over in the opposite direction from the initial tipping movement. Alternatively as the leg pivots inwardly, the weight of the-leg exerts a smaller torque resisting the tipping motion so that the motion may continue causing the unit to collapse. If instability of the support causes it to move, even where it does not fall over, accuracy is compromised.
It may be difficult to position the surveying pole in the correct location when a support is attached to the pole and the legs of the support are in a stowed position. The legs can obstruct the surveyor's view of the bottom point of the pole. It is desirable for the legs to be capable of retracting to a short length to reduce the obstruction. However, any items attached to the lower ends of the legs to facilitate securing the ends in the ground project down below the lower ends, increasing the effective retracted length of the leg and making it more difficult to remove the items as an obstruction by retracting the length of the legs.
Although the present invention has particular application for use in supporting surveying and geographic positioning equipment, it is not limited to such applications. As used herein “geomatic” is intended to encompass surveying and geographic positioning. The invention is envisioned as being useful to support equipment and other items having no relation to surveying or geographic positioning.